# std::is_swappable_with, std::is_swappable, std::is_nothrow_swappable_with, std::is_nothrow_swappable

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< cpp‎ | types

Defined in header `<type_traits>` |  |
template< class T, class U > struct is_swappable_with; | (1) | (since C++17)
template< class T > struct is_swappable; | (2) | (since C++17)
template< class T, class U > struct is_nothrow_swappable_with; | (3) | (since C++17)
template< class T > struct is_nothrow_swappable; | (4) | (since C++17)

1) If the expressions swap(std::declval<T>(), std::declval<U>()) and swap(std::declval<U>(), std::declval<T>()) are both well-formed in unevaluated context after using std::swap; (see Swappable), provides the member constant `value` equal true. Otherwise, `value` is false.
Access checks are performed as if from a context unrelated to either type.
3) Same as (1), but evaluations of both expressions from (1) are known not to throw exceptions.

Type trait | The value of the member constant `value`
--- | ---
`T` is a referenceable type | `T` is not a referenceable type
(2) | std::is_swappable_with<T&, T&>::value | false
(4) | std::is_nothrow_swappable_with<T&, T&>::value

If `T` or `U` is not a complete type, (possibly cv-qualified) void, or an array of unknown bound, the behavior is undefined.

If an instantiation of a template above depends, directly or indirectly, on an incomplete type, and that instantiation could yield a different result if that type were hypothetically completed, the behavior is undefined.

If the program adds specializations for any of the templates described on this page, the behavior is undefined.

### Helper variable templates

template< class T, class U > inline constexpr bool is_swappable_with_v = is_swappable_with<T, U>::value; |  | (since C++17)
template< class T > inline constexpr bool is_swappable_v = is_swappable<T>::value; |  | (since C++17)
template< class T, class U > inline constexpr bool is_nothrow_swappable_with_v = is_nothrow_swappable_with<T, U>::value; |  | (since C++17)
template< class T > inline constexpr bool is_nothrow_swappable_v = is_nothrow_swappable<T>::value; |  | (since C++17)

## Inherited from std::integral_constant

### Member constants

value [static] | true if `T` is swappable with `U`, false otherwise (public static member constant)

### Member functions

operator bool | converts the object to bool, returns value (public member function)
operator() (C++14) | returns value (public member function)

### Member types

Type | Definition
`value_type` | bool
`type` | std::integral_constant<bool, value>

### Notes

This trait does not check anything outside the immediate context of the swap expressions: if the use of `T` or `U` would trigger template specializations, generation of implicitly-defined special member functions etc, and those have errors, the actual swap may not compile even if std::is_swappable_with<T, U>::value compiles and evaluates to true.

### Example

| This section is incomplete Reason: no example

### See also

swap | swaps the values of two objects (function template)
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) | checks if a type has a move assignment operator (class template)
swappableswappable_with (C++20) | specifies that a type can be swapped or that two types can be swapped with each other (concept)

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